Backpack



FIG. 1 is a front, left perspective view of an embodiment of a backpack showing my new design.

FIG. 2 is a front view of the backpack.

FIG. 3 is a rear view of the backpack.

FIG. 4 is a left side view of the backpack.

FIG. 5 is a right side view of the backpack.

FIG. 6 is a top view of the backpack; and,

FIG. 7 is a bottom view of the backpack.

The broken lines are environmental only and form no part of the claimed design. 

The ornamental design for a backpack, as shown and described. 